The study was conducted using lactating cows grazing a lush oat (Avena sativa) pasture for at least 8 h/d, and receivingthe rest of the diet as a corn silage-based partial mixed ration (PMR) plus some dry rolled grain at milking. These routinemanagement procedures are representative of many dairy farms in Argentina, and other parts of the world where grazing isa management tool for lactating dairy cows. To our knowledge, this is the first published report on supplementing grazinganimals with this EO complex, thus it was not possible to make direct comparisons to similar studies. Consequently, com-parisons were made with studies that used non-grazing cows or cows receiving other EO compounds, which may be of onlylimited relevance.Milk production yields were lower than expected based on estimated DM intake and diet chemical composition. Inaddition, there was a quadratic change in body weight, which is difficult to interpret with the available evidence. However